They harrasing me

I m having account with Lewis furniture Pietermaritzburg church street change my bank account and gave them new account number but they failed to deduct the money. And they handed me over for collection, I told them to call me for Debi check and I approved Debi check but still they harassing me coming to my work place telling me I need to pay the outstanding amount and still receiving calls from their collection company they telling me that Lewis handed me on other side Lewis calling me everyday after made new arrangements. They harrasing me now and I am confused what to do now.